Centrifugal turbomachine

ABSTRACT

A plurality of vaned diffusers is disposed on a concentric plate at intervals in a circumferential direction thereof, and each of the diffusers is a curvilinear element three-dimensional diffuser having blades which are extended from a hub side of a impeller to a shroud side thereof. The blades are formed in a form in which a blade serving as a reference is stacked in a direction of the height of the blade, which is a direction of a gap between the hub and the shroud. A dihedral distribution in which moving in a direction perpendicular to a chord direction linking a leading edge of the blade as the reference with a tailing edge thereof, is set as a positive movement is non-uniform from an end portion on the hub side to an intermediate portion of the height of the blade.

TECHNICAL FIELD

The present invention relates to a centrifugal turbomachine including acentrifugal impeller, such as a centrifugal compressor, centrifugalblower, centrifugal fan or centrifugal pump.

BACKGROUND ART

The multistage centrifugal compressor, a kind of centrifugalturbomachine, has a number of impellers mounted on the same shaft. Adiffuser and a return guide vane are installed side by side downstreamof each of the impellers. The impeller, the diffuser, and the returnguide vane constitute a stage. Here, a vaneless diffuser, a vaneddiffuser, a low solidity diffuser that is a kind of the vaned diffuser,or the like, is used as the diffuser, depending on the purpose andintended use.

Among these diffusers, the low solidity diffuser has the property ofbeing able to increase the choke margin that is the operating range on ahigh flow side, because it does not have a geometrical throat. Also, thelow solidity diffuser has the advantage of being able to sufficientlyensure the surge margin that is the operating range on a low flow side,because separation on the blade surface in a low flow area is suppressedby the effect of a secondary flow which sweeps the boundary layer on theblade surface. For this reason, the low solidity diffuser is frequentlyused.

A 2D blade with the same blade profiles stacked in a blade heightdirection is commonly used for a vaned diffuser for centrifugalturbomachines as typified by the low solidity diffuser. However, inresponse to the demands for a further performance improvement, attemptsare also being made to use a 3D blade. For example, in a centrifugalcompressor disclosed in Patent Literature 1, the stagger angle of adiffuser blade section is gradually varied in the blade height directionof the diffuser to form the 3D blade, thereby realizing a collisionlessflow for an unevenly distributed inflow and achieving both of animprovement in efficiency and an increase in operating range.

Furthermore, in a centrifugal compressor disclosed in Patent Literature2, a diffuser inlet diameter is changed by bending downstream aheightwise central portion of a blade at a leading edge portion of adiffuser. Thus, a collision-free flow for the unevenly distributedinflow is realized and both of an improvement in efficiency and anincrease in operating range are achieved.

CITATION LIST Patent Literature

-   Patent Literature 1: JP-A No, 2009-504974-   Patent Literature 2: JP-A No. 2004-92482

SUMMARY OF INVENTION Technical Problem

In the airfoil diffuser for the centrifugal compressor disclosed in theabove-described Patent Literature 1, a 3D diffuser blade is formed bystacking divided diffuser blades virtually in an axial direction(direction from a hub plane to a shroud plane). At this time, there isalso suggested a bow diffuser blade in which a lean angle is variedalong a diffuser blade span, the lean angle meaning the angle which thestacking direction of the blades makes with the direction perpendicularto the hub or shroud plane.

However, the authors consider that the curvilinear element blade doesnot necessarily lead to sufficient improvements because many options areavailable. That is, if lean distribution is applied to the blade, thesecondary flow might be increased by its application, resulting inperformance deterioration. Therefore, there is a need for clarificationof the stacking pattern of divided blades which leads to performanceimprovement.

Furthermore, in the centrifugal compressor disclosed in the PatentLiterature 2, lean is applied to a local portion, namely, the diffuserleading edge to achieve inflow angle matching. However, any constructionof the curvilinear element diffuser is not adopted, and no considerationis given to control of the secondary flow in a flow path betweendiffuser blades which becomes more conspicuous when the curvilinearelement diffuser is employed.

The present invention has been made in view of problems of the relatedart described above, and an object of the present invention is toprovide effectively suppress a secondary flow between blades and improveperformance when a curvilinear element diffuser is used to increaseefficiency in a vaned diffuser for use in a centrifugal turbomachine.Another object of the present invention is to obtain a stacking patternof divided blades which leads to performance improvement, in thecurvilinear element diffuser for use in a centrifugal turbomachine.

Solution to Problem

Firstly, referring to FIGS. 1 and 2, some terms used in thisspecification will be defined as follows. FIG. 1 is a plan view of onediffuser blade for explaining the movement of a blade profile. FIG. 2 isa perspective view of one blade taken from a vaned diffuser, showing thestate in which basic blade profiles are stacked in a Z direction. Acoordinate system is a cylindrical coordinate system (R, θ, Z), in whichthe radial direction of an impeller is denoted by R, the direction ofrotation of the impeller is denoted by θ, and the axial direction of arotating shaft is denoted by Z. The Z direction from a shroud 102 to ahub 101 is set as positive.

Chord (C): line that connects a leading edge 208 and a trailing edge 209of a blade profile 104 serving as a basis of a diffuser blade 103.

Lean: degree of tilt of the diffuser blade 103 relative to the surfaceof the hub 101, and it can be regarded as a combination of sweep anddihedral to be described below.

Stagger Angle (θ_(SG)): angle (tan θ_(SG)=dC/dR) which the chord C formswith the radial direction (R direction).

Sweep (Δσ): as indicated by alternate long and short dashed lines inFIG. 1, to move the blade profile 104 of the diffuser blade 103 parallelto the direction of the chord C. The movement in a downstream directionis set as positive.

Dihedral (Δδ): as indicated by dashed lines in FIG. 1, to move the bladeprofile 104 of the diffuser blade 103 in the direction perpendicular tothe chord C. The movement in the opposite direction of rotation of theimpeller is set as positive.

Blade Height (h): height of the diffuser blade, the height beingmeasured from the hub surface. If the hub and shroud surfaces areparallel walls normal to the axis, the blade height is the height in thenegative Z direction. If at least one of the hub and shroud surfacesincludes a tilted surface, the blade height is the height measured froma line that connects the leading edge and the trailing edge on the hubside of the diffuser blade. The height of an intermediate point in aflow direction between the leading edge and the trailing edge isdetermined with reference to a line that connects the leading edges onthe hub and shroud sides of the diffuser blade and a line that connectsthe trailing edges on the hub and shroud sides of the diffuser blade.The total height of the blades is represented by H.

Using these definitions, in order to address the above-describedproblems, the present invention provides a centrifugal turbomachineincluding: at least one or more impellers attached to an identicalrotating shaft and composed of a hub, a shroud, and a plurality ofcircumferentially spaced apart blades between the hub and the shroud;and a vaned diffuser disposed downstream of at least one of theimpellers, wherein: the vaned diffuser includes a plurality ofcircumferentially spaced apart blades in a flow passage that is formeddownstream of the impeller, each of the blades being formed with basicblade profiles stacked in a blade height direction that corresponds toan axial direction of the rotating shaft; and dihedral distribution inwhich movement in a direction perpendicular to a chord directionconnecting leading and trailing edges of each of the basic bladeprofiles and in an opposite direction of rotation of the impeller is setas positive is made uneven from a hub-side end to an intermediateportion in the blade height direction on a hub wall surface side.

Also in this feature, preferably, the dihedral distribution of each ofthe diffuser blades is increased from the hub-side end to theintermediate portion in the blade height direction, and, in each of thediffuser blades, an angle between a plane virtually formed at a leadingedge portion on the hub-side end and a suction surface of the diffuserblade is an obtuse angle.

Furthermore, preferably, the dihedral distribution increases from ashroud-side end to the intermediate portion in the blade heightdirection, and, in each of the diffuser blades, an angle between a planevirtually formed at the leading edge portion on the shroud-side end andthe suction surface of the diffuser blade is an obtuse angle.

In the above-described feature, the arrangement may be such that thedihedral distribution of each of the diffuser blades decreases from thehub-side end to the intermediate portion in the blade height direction,and sweep distribution in which movement in a direction parallel to thechord direction of the basic blade profiles and in a downstreamdirection is set as positive is decreased from the hub-side end to theintermediate portion in the blade height direction.

It should be noted that, in any of the above-described features,preferably, at least one of the dihedral distribution and the sweepdistribution is applied to at least a first half portion in a flowdirection of the diffuser blades.

Advantageous Effects of Invention

According to the present invention, in the vaned diffuser for use in thecentrifugal turbomachine, the 3D curvilinear-element blade is applied tothe diffuser blade, and the sweep and dihedral distributions are given,thereby reducing the loss due to the collision of the flow with thediffuser blade. Furthermore, because the flow at the intermediateportion of the blade can be controlled, the secondary flow between theblades is effectively suppressed and the diffuser performance and thecompressor performance can be improved. Moreover, in the presentinvention, in this curvilinear-element diffuser for use in thecentrifugal compressor, a stacking pattern of divided blades which leadsto performance improvement can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating tilting in a vaned diffuser.

FIG. 2 is a view illustrating a 3D blade included in the vaned diffuser.

FIG. 3 is a longitudinal sectional view of one embodiment of acentrifugal turbomachine according to the present invention.

FIG. 4 is a view illustrating the classification of vaned diffusers.

FIG. 5 is a graph illustrating dihedral distribution, according to oneembodiment, of the diffuser included in a compressor shown in FIG. 3.

FIG. 6 is a perspective view of the diffuser having the dihedraldistribution shown in FIG. 5, and a partially-enlarged view thereof.

FIG. 7 is a graph illustrating dihedral distribution, according toanother embodiment, of the diffuser included in the compressor shown inFIG. 3.

FIG. 8 is a perspective view of the diffuser having the dihedraldistribution shown in FIG. 7, and a partially-enlarged view thereof.

FIG. 9 is a graph illustrating dihedral and sweep distributions,according to still another embodiment, of the diffuser included in thecompressor shown in FIG. 3.

FIG. 10 is a perspective view of the diffuser having the dihedral andsweep distributions shown in FIG. 9, and a partially-enlarged viewthereof.

FIG. 11 is an exemplary performance diagram of the centrifugalcompressor including the diffuser according to the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, several embodiments of the present invention will bedescribed by using the accompanying drawings. Firstly, a multistagecentrifugal compressor 300 serving as an example of a centrifugalturbomachine will be described by using a longitudinal sectional view ofFIG. 3. The multistage centrifugal compressor 300 is a two-stagecentrifugal compressor. It should be noted that the subject of thepresent invention is not particularly limited to the two-stagecentrifugal compressor, but also can include single-stage or multistagecentrifugal turbomachines.

The multistage centrifugal compressor 300 shown in FIG. 3 is thetwo-stage centrifugal compressor that is composed of a first stage 301and a second stage 302. A first-stage impeller 308 and a second stageimpeller 311 are attached to an identical rotating shaft 303 toconstitute a rotating body. The rotating shaft 303 is rotatablysupported by a journal bearing 304 and a thrust bearing 305 that areattached to a compressor casing 306 for storing the rotating shaft 303and the impellers 308 and 311.

Downstream of the first-stage impeller 308, there are disposed adiffuser 309 that recovers the pressure of working gas compressed by theimpeller 308 and forms a radially outwardly directed flow, and a returnguide vane 310 that directs radially inwardly the radially outward flowof working gas caused by the diffuser 309 and guides it to thesecond-stage impeller 311. Downstream of the second-stage impeller 311,a diffuser 312 is similarly disposed, and recovery means 313, called acollector or scroll, for gathering and sending out the working gassubjected to pressure rise by the second-stage diffuser 312 is disposed.

The first- and second-stage impellers 308 and 311 have hub-side plates308 a and 311 a, shroud-side plates 308 b and 311 b, and a plurality ofblades 308 c and 311 c arranged circumferentially with almost equalspacing between the core plate 308 a and the side plate 308 b andbetween the core plate 311 a and the side plate 311 b, respectively.Labyrinth seals 315 are disposed at outer peripheral portions of theshroud-side plates 308 b and 311 b on the entrance sides of theimpellers 308 and 311. Also, shaft seals 316 and 317 are disposed at therear of the hub-side plates 308 a and 311 a. Working gas flowing from asuction nozzle 307 passes in order through the first-stage impeller 308,the vaned diffuser 309, the return guide vane 310, the second-stageimpeller 311, and the vaned diffuser 312, and is guided without leakageto the recovery means 313 such as the collector or scroll.

The diffusers 309 and 312 for use in the centrifugal compressor 300 asconstructed in this manner will be described in detail below. It shouldbe noted that the diffuser 309 is attached to a diaphragm constituting aportion of the compressor casing 306 and has a hub 309 a with a passageplane located at almost the same axial position as that of the impeller308 and a plurality of circumferentially-spaced-apart blades 309 cprovided in a standing manner on the surface of the hub 309 a.Furthermore, the wall surface of an inner casing constituting a portionof the compressor casing 306 forms a flow passage as a shroud surface.Although not descried here, the diffuser 312 has the same construction.It should be noted that, although the above construction is described inthis embodiment, the construction of the diffuser is not limitedthereto. The present invention, of course, also includes theconstruction being such that the diffuser is separate from thediaphragm.

In FIG. 4, vaned diffusers 400 to be used in the following descriptionare classified and shown. FIG. 4( a) is a cross-sectional view of thediffuser 400. A plurality of diffuser blades 420 a arrangedcircumferentially with almost equal spacing are provided in a standingmanner on a hub plate 410 a. The flow from the impeller, which is notshown, is guided so as to flow along the diffuser blades 420 a from theinner periphery as indicated by arrow FL in the drawing. At this time,the impeller, not shown, rotates in the direction of arrow R_(N).

The shapes of the diffuser are classified into: a 2D diffuser which hasconventionally been employed (FIG. 4( b)); a 3D straight-line elementdiffuser having a lean (FIG. 4 (c)); and a 3D curvilinear-elementdiffuser also having a lean and represented by a set of curvilinearelements (FIG. 4( d)). Here, diffuser blades 420 b to 420 d arerepresented as a shape with linear elements 423 b to 423 d connectingthe contours of hub-plate-side sections 421 b to 421 d and shroud-sidesections 422 b to 422 d. The same flow is discharged from the impellerto the diffuser blades 420 b to 420 d to form a diffuser entry flow 402.

The 2D straight-line element diffuser blade 420 b shown in FIG. 4 (b) isa 2D diffuser that is formed of the straight-line element 423 b, nottilted, with the same blade profiles stacked straight in a heightdirection of the blade 420 b. That is, the straight-line element 423 bis perpendicular to the hub plate 410 a. In the diffuser having thisblade 420 b, it is impossible to prevent the flow from colliding withthe blade 420 b in all positions in the height direction (h direction)of a leading edge of the blade 420 b when the inlet flow 402 isdistributed, and there is a limit to the improvement in performance.

In the 3D straight-line element diffuser shown FIG. 4 (c), a twist isadded to the diffuser blade 420 c by varying the stagger angle (θ_(SG)).This allows the flow from the impeller to flow into the diffuser blade420 c without colliding with the diffuser blade 420 c. That is, even ifan uneven flow is discharged from the impeller, the shape at a leadingedge portion of the diffuser blade 420 c can be changed according to theinlet flow 402.

In this 3D straight-line element diffuser blade 420 c, the linearelement 423 c connecting the contours of the hub-plate-side section 421c and the shroud-side section 422 c is a straight line, and the leandistribution in the height direction (h direction) of the blade 420 calso has a linear design. However, the linear element 423 c is notnecessarily perpendicular to the hub plate 410 a. After entry of theflow between the blades 420 c and 420 c, the lean angle cannot bechanged to a value corresponding to a flow angle because the blade 420 cis formed, for example, in a basic NACA airfoil shape. Therefore,although a greater improvement in efficiency than the 2D diffuser can beexpected, sufficient flow control is difficult.

In the 3D curvilinear-element diffuser shown FIG. 4 (d), the bladeprofiles are stacked along the optional curvilinear element 423 d. Inother words, the curvilinear element 423 d connecting the contours ofthe hub-plate-side section 421 d and the shroud-side section 422 d is acurve line. In this diffuser, the lean angle is varied, rather thanbeing constant, in the height direction (h direction) of the blade 420d. Thus, with the 3D curvilinear-element diffuser, it is possible to notmerely realize a collision-free inflow at a leading edge portion of theblade 420 d but also change the direction of action of blade force bybending a passage plane of the blade 420 d.

Therefore, the flow in a flow passage between the blades 420 d and 420 dcan be controlled. Therefore, in the present invention, as shown in FIG.3, the diffusers 309 and 312 that recover the dynamic pressure at exitsof the impellers 308 and 311 as static pressure are made 3Dcurvilinear-element diffusers.

Meanwhile, although there are various methods for making the diffuserbeing three dimensional, the diffuser can be systematically made threedimensional by using the above-described dihedral and sweep. Therefore,a specific example of the 3D curvilinear-element diffuser representedusing the dihedral and sweep will be described by using FIGS. 5 to 11.In the following description, the first stage diffuser 309 is used as anexample. However, the second and subsequent stage diffusers are alsoused in the same manner.

One embodiment of the 3D curvilinear-element diffuser will be describedby using FIGS. 5 and 6. Only the dihedral distribution is shown. FIG. 5is a graph illustrating dihedral distribution in a blade heightdirection (h direction) of a blade 620, in which the amount of dihedral(Δδ) is made dimensionless with the chord length (C) and the bladeheight is made dimensionless with the total height H. FIG. 6 is aperspective view of a diffuser 600 having the dihedral distribution ofFIG. 5, in which FIG. 6( a) is a general perspective view; FIG. 6( b) isa detail view of portion C in FIG. 6( a); and FIG. 6( c) is a detailview of portion D in FIG. 6( a). A diffuser plate 610 is attached to thehub side of the impeller.

As shown in FIG. 5, in this embodiment, the dihedral increases in theblade height direction in the vicinity of a hub-side end face (h=0) (seea portion 501 surrounded by a circle). That is, a suction surface 601 ofthe diffuser blade 620 forms an obtuse angle with a hub surface 603. Itshould be noted that the suction surface 601 of the diffuser blade 620corresponds to the blade surface that is located to the rear withrespect to the direction of rotation of the impeller.

Studies by the inventors of the present invention showed that, in thedihedral distribution shown in FIG. 5, the influence of the dihedral orsweep distribution on performance was generally small in a portion otherthan the portion 501 surrounded by a circle, that is, the portion 501 inthe vicinity of the hub-side end face. Therefore, the dihedral and sweepdistributions can be set in the portion other than the portion 501 inthe vicinity of the hub-side end face in consideration of theworkability or handleability of the blades 309 c.

As shown in FIG. 6( b), in the diffuser 600 of this embodiment, a bladeforce component 602 is generated in the blade height direction. Theblade force component 602 has the effect of forcing back the secondaryflow because a boundary layer on the hub surface 603 is located in theopposite direction of the secondary flow that tends to migrate towardthe hub-side suction surface 601. Thus, according to this embodiment,the secondary flow is suppressed, leading uniform distribution of theflow between the blades and an improvement in diffuser performance.

Another embodiment of the present invention will be described by usingFIGS. 7 and 8. These drawings are the same as those of theabove-described embodiment. FIG. 7 is a graph of dihedral distribution,and FIG. 8 is a perspective view of a diffuser 800 having the dihedraldistribution shown in FIG. 7. FIG. 8( a) is a general perspective viewof the diffuser 800; FIG. 8( b) is a detail view of portion E in FIG. 8(a); and FIG. 8( c) is a detail view of portion F in FIG. 8( a). Also inthe diffuser 800, a diffuser plate 810 is attached to the hub side ofthe impeller. This embodiment differs from the above-describedembodiment in that the dihedral is reduced in the blade height directionin the vicinity of a shroud-side end face (a portion 702 surrounded by acircle).

Although in the above-described embodiment, the influence of thedihedral distribution is greater on the hub-surface side, it has turnedout that the dihedral distribution on the shroud-surface side alsoexerts an influence upon the diffuser according to the flow from theimpeller. It should be noted that, even in this case, the dihedraldistribution on the shroud side should be the same as theabove-described embodiment. A specific example thereof will be describedbelow.

On the hub-side end face, the amount of dihedral (Δδ) is increased inthe blade height direction (h direction) in the same manner as theabove-described embodiment (see a portion 701 surrounded by a circle).Also in this embodiment, the influence of the dihedral or sweepdistribution on performance is small in a center region in the bladeheight direction other than the two regions in the vicinity of thehub-side end face and the shroud-side end face. That is, in the vicinityof the hub-side and shroud-side end faces, the angle that suctionsurfaces 801 and 802 of a diffuser blade 820 form with the hub andshroud end faces is an obtuse angle. Therefore, the secondary flow canbe suppressed by the same working effects as the above-describedembodiment.

It should be noted that the distribution shown in FIG. 7 is preferablyused if the flow at the exit of the impeller is relatively uniform,while the distribution shown in FIG. 5 is preferably used if thenonuniformity is high. This is because the diffuser blade 820 isaffected by the uniformity or nonuniformity of the flow at the exit ofthe impeller. That is, if the nonuniformity of the flow at the exit ofthe impeller is high, a high-energy portion of the flow is controlled byfocusing on the flow control on the hub-surface side on where themainstream exists, and consequently the overall flow can be effectivelycontrolled.

Still another embodiment of the present invention will be described byusing FIGS. 9 and 10. FIG. 9( a) is a graph of dihedral distribution,and FIG. 9( b) is a graph of sweep distribution which is madedimensionless with the chord length. FIG. 10 is a perspective view ofthe diffuser 309 having the distributions shown in FIG. 9, in which FIG.10( a) is a general view of the diffuser; FIG. 10( b) is a detail viewof portion G in FIG. 9( a); and FIG. 10( c) is a detail view of portionH in FIG. 9( a). In the same manner as the above-described embodiments,a diffuser plate 1010 is attached to the hub side of the impeller.

In the above-described two embodiments, the dihedral distribution on thehub side is important, and the increase in dihedral in the blade heightdirection is effective from the viewpoint of flow control. However, ithas turned out that the combination of dihedral and sweep providesbenefits even when the dihedral is reduced in the blade heightdirection. A specific example thereof will be described below.

As shown in FIG. 9, in this embodiment, the dihedral is reduced in theblade height direction in the vicinity of the hub-side end face (see aportion 901 surrounded by a circle), and furthermore, the sweep isreduced similarly in the vicinity of the hub-side end face (see aportion 902 surrounded by a circle). That is, the diffuser has a leanwith the dihedral and sweep combined and is a diffuser 1000 in which the3D curvilinear-element is used. Because the effects on performance aresmall in a region other than the vicinity of the hub-side end face, bothdihedral and sweep can be arbitrarily set, as long as an extreme changeis not caused.

In this embodiment, the direction of the dihedral on the hub-side endface is the reverse of those of the above-described embodiments. As aresult, the angle formed by a diffuser suction surface 1001 and thesurface of a hub plate 1010 is an acute angle, and a blade forceopposite in direction to the blade force component 602 shown in FIG. 6is generated. This reversed blade force appears to increase thesecondary flow, but actually serves to suppress the secondary flow. Thereason is as follows.

In this embodiment, a diffuser blade 1020 is composed of a combinationof dihedral and sweep. Because the diffuser blade 1020 has a sweep 1002,a notch-shaped gap 1003 is formed between a leading edge 1005 of thediffuser blade 1020 and the surface of the hub plate 1010. In thenotch-shaped gap 1003, a flow that tends to migrate from the pressuresurface to the suction surface of the diffuser blade 1020 occurs,thereby generating a longitudinal vortex 1004. Vorticity 1006 tosuppress the secondary flow is generated in a corner formed by thesuction surface of the diffuser blade 1020 and the surface of the hubplate 1010. At the same time, separation on the blade surface in thediffuser blade 1020 is suppressed by the promotion of agitation with thesurrounding fluid or the negative pressure effect of the vortex center.In this manner, the secondary flow is suppressed by the action of thelongitudinal vortex, and the flow field is made uniform, therebyimproving the performance of the 3D curvilinear-element diffuser.

FIG. 11 shows a state in which the compressor performance is improvedwhen the 3D curvilinear-element diffuser shown in this embodiment isused in place of the 2D straight-line element diffuser in a compressor.The horizontal axis of the graph represents flow rate Q madedimensionless with design point flow rate Qdes, and the vertical axisrepresents: adiabatic efficiency η of the compressor stage madedimensionless with adiabatic efficiency η_(2DIM) in the 2D diffuser; andpressure coefficient ψ made dimensionless with pressure coefficientψ_(2DIM) in the 2D diffuser.

The adiabatic efficiency η and the pressure coefficient ψ are improvedover a wide flow range, not to mention the design flow rate. Also, thevaned diffuser according to the present invention is superior inperformance at an off design point (Q≠ 1.0) because the amount ofperformance improvement increases with distance from the design pointflow rate (Q=1.0). That is, the compressor operating range is improved.

In the above-described embodiments, the diffuser blade has at least oneof sweep distribution and dihedral distribution, thereby realizing the3D curvilinear-element diffuser. Furthermore, the secondary flow in thevicinity of a hub wall surface and a shroud wall surface of the diffuserand the impinging flow near the leading edge of the diffuser blade arecontrolled by inclining the diffuser blades. As a result, the diffuserperformance can be improved. It should be noted that the sweep anddihedral distributions shown in the above-described embodiments are justan example and, also in the region that is not limited in shape becausethe influence on performance is small, the sweep and dihedraldistributions are illustrative only.

Furthermore, although preferably, the entire blades have the shapefeature shown in the embodiments, the advantages of the presentinvention can be obtained even if the blades have the above-describedshape especially only in a first half portion in the flow direction ofthe diffuser because the shapes in the first half portion (upstream) ofthe diffuser blades have a relatively great influence on performance.Therefore, the 2D straight-line element diffuser or the like, which hasbeen conventionally frequently employed, may be used for a latter halfportion in the flow direction.

Although in the above-described embodiments, the diffuser blades areprovided on the hub plate, the diffuser blades may be of course providedon the surface thereof facing the hub plate, that is, the plate on theshroud-surface side. In any case, the diffuser blades are mounted on thehub or shroud side for ease of assembly, etc. Further, there is no needfor the multistage compressor to be entirely provided with vaneddiffusers. Even if a vaned diffuser is provided on at least one stage ofthe compressor and the present invention is applied to the diffuser, theadvantages of the present invention can be obtained.

REFERENCE SINGS LIST

-   101 Hub-   102 Shroud-   103 Diffuser blade-   104 Blade profile-   105 Diffuser plate-   208 Leading edge-   209 Trailing edge-   300 Centrifugal turbomachine (multistage centrifugal compressor)-   301 First stage-   302 Second stage-   303 Rotating shaft-   304 Journal bearing-   305 Thrust bearing-   306 Compressor casing-   307 Suction nozzle-   308 First-stage impeller-   308 a Hub-side plate-   308 b Shroud-side plate-   308 c Blade-   309 Vaned diffuser-   309 a Hub-   309 c Blade-   310 Return guide vane-   311 Second-stage impeller-   311 a Hub-side plate-   311 b Shroud-side plate-   311 c Blade-   312 Vaned diffuser-   313 Recovery means (scroll or collector)-   315 Labyrinth seal-   316, 317 Shaft seal-   400 Vaned diffuser-   401 Straight-line element-   402 Inlet flow-   403 Hub-side blade section-   404 Shroud-side blade section-   405 Straight-line element-   407 Hub-side blade section-   408 Shroud-side blade section-   409 Curvilinear element-   410 Hub plate-   411 Hub-side blade section-   412 Shroud-side blade section-   420 a to 420 d Diffuser blade-   421 b to 421 d Hub surface-   422 b to 422 d Shroud surface-   423 b to 423 d Linear element-   501 Dihedral distribution-   600 Vaned diffuser-   601 Hub-side suction surface-   602 Blade force component-   603 Hub surface-   610 Hub plate-   620 Blade-   701 Dihedral distribution-   702 Dihedral distribution-   800 Vaned diffuser-   801 Hub-side suction surface-   802 Shroud-side suction surface-   810 Hub surface-   820 Blade-   901 Dihedral distribution-   902 Sweep distribution-   1000 Vaned diffuser-   1001 Hub-side suction surface-   1002 Sweep-   1003 Notch-   1004 Longitudinal vortex-   1005 Diffuser leading edge-   1006 Vorticity-   1010 Hub plate-   1020 Blade-   C Chord-   FL Inlet flow-   h Height of diffuser blade-   H Total height of diffuser blades-   R_(N) Direction of rotation of impeller-   Δδ Amount of dihedral-   Δσ Amount of sweep-   Q Flow rate-   Qdes Design point flow rate-   η Adiabatic efficiency-   η_(2DIM) Efficiency of 2D blade diffuser-   ψ Pressure coefficient-   ψ_(2DIM) Pressure coefficient of 2D blade diffuser

1. A centrifugal turbomachine comprising: at least one or more impellers attached to an identical rotating shaft and composed of a hub, a shroud, and a plurality of circumferentially spaced apart blades between the hub and the shroud; and a vaned diffuser disposed downstream of at least one of the impellers, wherein: the vaned diffuser includes a plurality of circumferentially spaced apart blades in a flow passage that is formed downstream of the impeller, each of the blades being formed with basic blade profiles stacked in a blade height direction that corresponds to an axial direction of the rotating shaft; and dihedral distribution in which movement in a direction perpendicular to a chord direction connecting leading and trailing edges of each of the basic blade profiles and in an opposite direction of rotation of the impeller is set as positive is made uneven from a hub-side end to an intermediate portion in the blade height direction on a hub wall surface side.
 2. The centrifugal turbomachine according to claim 1, wherein the dihedral distribution of each of the diffuser blades is increased from the hub-side end to the intermediate portion in the blade height direction.
 3. The centrifugal turbomachine according to claim 2, wherein, in each of the diffuser blades, an angle between a plane virtually formed at a leading edge portion on the hub-side end and a suction surface of the diffuser blade is an obtuse angle.
 4. The centrifugal turbomachine according to claim 3, wherein the dihedral distribution increases from a shroud-side end to the intermediate portion in the blade height direction and from the hub-side end to the intermediate portion in the blade height direction.
 5. The centrifugal turbomachine according to claim 4, wherein, in each of the diffuser blades, angles between a plane virtually formed at the leading edge portion on the shroud-side end and the suction surface of the diffuser blade and between a hub plate and the suction surface of the diffuser blade are each an obtuse angle.
 6. The centrifugal turbomachine according to claim 1, wherein the dihedral distribution of each of the diffuser blades decreases from the hub-side end to the intermediate portion in the blade height direction, and sweep distribution in which movement in a direction parallel to the chord direction of the basic blade profiles and in a downstream direction is set as positive is decreased from the hub-side end to the intermediate portion in the blade height direction.
 7. The centrifugal turbomachine according to claim 1, wherein at least one of the dihedral distribution and the sweep distribution is applied to at least a first half portion in a flow direction of the diffuser blades.
 8. The centrifugal turbomachine according to claim 2, wherein at least one of the dihedral distribution and the sweep distribution is applied to at least a first half portion in a flow direction of the diffuser blades.
 9. The centrifugal turbomachine according to claim 3, wherein at least one of the dihedral distribution and the sweep distribution is applied to at least a first half portion in a flow direction of the diffuser blades.
 10. The centrifugal turbomachine according to claim 4, wherein at least one of the dihedral distribution and the sweep distribution is applied to at least a first half portion in a flow direction of the diffuser blades.
 11. The centrifugal turbomachine according to claim 5, wherein at least one of the dihedral distribution and the sweep distribution is applied to at least a first half portion in a flow direction of the diffuser blades.
 12. The centrifugal turbomachine according to claim 6, wherein at least one of the dihedral distribution and the sweep distribution is applied to at least a first half portion in a flow direction of the diffuser blades. 